Study On The Synergistic Action Mechanism Of Dimethyl Dicarbonate And Nisin Against The Microorganisms Of Litchi Juice And Its Application

Dimethyl carbonate(DMDC) has become one of the emerging non-thermal sterilization technology research hot spot, because of its low cost, easy operation, safety, and shall not affect the flavor and taste of products when compared with other sterilization technology.But some studies found that DMDC bactericidal effect for bacteria pollution in fruit juice are significant differences, some certain lactic acid bacteria has strong tolerance to DMDC, therefore, if only use DMDC in the fresh juice,the sterilization effect is usually not ideal. Nisin is an amino acid peptide active substances, can effectively kill or inhibit food corruption caused by gram-positive bacteria, especially bacterial spores. Early research has shown that DMDC combined with Nisin has good synergistic bactericidal action for DMDC tolerance bacteria in litchi juice. According to the different sterilization characteristics of DMDC and Nisin, we mainly studied the bactericidal effect and its sterilization mechanism of DMDC and Nisin in litchi juice; and evaluate the change rule of quality in litchi juice after treated with DMDC and Nisin during stored at 4℃,in order to provide reference for the application of DMDC combined with Nisin sterilization in litchi juice. Main conclusions are as follows:1. Analyzed the antiseptic properties of DMDC in litchi juice, at the same time, separated and identified the resistant microorganisms. The study found that the increase of temperature can improve the sterilization rate of DMDC, shortening the sterilized time, but cannot improve overall sterilization effect. After treated with DMDC,the residual pollution bacteria in litchi juice mainly bacillus genus, mucor and leuconostoc strains, and Leuconostoc is advantage bacterium group among the bacteria.2. Assessing the sterilization effect of DMDC combined with Nisin for L.mesenteroides, B.subtilis and E.coli three bacteria in litchi juice used fractional bactericidal concentration(FBC) index. The results show that DMDC and nisin had strong synergistic effect on the inactivation of L.mesenteroides and B.subtilis, and had irrelevant effect on the inactivation of E.coli.3. Inactivation of Leuconostoc mesenteroides and changes of its membrane function were investigated as treated with dimethyl carbonate(DMDC) and nisin. It was found that a synergistic bactericidal effect existed between DMDC and nisin. No obvious changes were observed in the cell morphology of Leuconostoc mesenteroides treated with DMDC and Nisin. A synergistic effect on the increase of membrane permeability, the loss of intracellular substances, and the decrease of intracellular pH was not found between DMDC and nisin, and a synergistic effect on the inactivion of dehydrogenase was showed between DMDC and nisin. Studying the change of bacteria protein modification degree after treated with Nisin and DMDC, we found that Nisin did not significantly enhance the modification degree of DMDC on bacteria protein, there only a little facilitation.4. DMDC combined with Nisin sterilization,which was equivalent to the heat sterilization treatment(95℃, 1 min),can ensure the microbiological safe of litchi juice during storage at 4°C. Compare with heat treatment, the treatment of DMDC combined with Nisin can retain a more value of sensory attributes, but a more loss in the content of total phenicals, ascorbic acid, and antioxidant capacity was observed during storage at 4°C because of the ineffectiveness of DMDC and Nisin to the oxidase of litchi juice. Moreover, the litchi juice treated by DMDC and Nisin gradually turned into light red at the end of storage because of the oxidation of phenicls by residual POD in the litchi juice, which resulted in a significant changes(P<0.05) in the value of L?, a?, b?, and △E compare with heat treatment in the litchi juice. After isolation and extraction of phenolics in litchi juice for the whole storage, we found that browning in litchi juice during storage is mainly caused by the oxidation of soluble combination phenol and free phenol. So DMDC combined with Nisin treatment offers a useful alternative to conventional heat for controlling microbial growth and significantly extending the shelf-life of litchi juice as only considering the inactivation and inhibition of indigenous microorganism.